1. Field of the Invention
This invention relates to vena cava filters and like devices and more particularly to delivery systems for such devices.
2. Description of Related Art
A vena cava filter is one species of expansible devices that can be inserted percutaneously into a human. Stents, retrieval baskets and grasping devices constitute other species of such expansible devices. A delivery system generally transports such a device in a compact form to a placement site in a particular vessel. Manipulation of controls associated with the delivery system causes or enables the device to expand into a final configuration within the vessel. Although delivery system will have the foregoing characteristics in common, any delivery systems for a specific device will have particular features for optimizing its operation with a specific device.
For example medical stents, as known, serve as protheses and graft carriers during percutaneous angioplasty procedures. Corresponding stent delivery systems generally include catheters with selectively expansible devices to deliver and either expand a compacted stent or allow the stent to expand. The following patents disclose such stent delivery systems.
U.S. Pat. No. 4,922,905 (1990) Strecker PA1 U.S. Pat. No. 4,950,227 (1990) Savin et al. PA1 U.S. Pat. No. 4,590,938 (1986) Segura et al. PA1 U.S. Pat. No. 4,611,594 (1986) Grayhack et al. PA1 U.S. Pat. No. 3,952,747 (1976) Kimmell, Jr. PA1 U.S. Pat. No. 4,425,908 (1984) Simon PA1 U.S. Pat. No. 4,793,348 (1988) Palmaz PA1 U.S. Pat. No. 4,817,600 (1989) Herms et al. PA1 U.S. Pat. No. 4,832,055 (1989) Palestrant PA1 U.S. Pat. No. 5,300,086 (1994) Gory et al.
In Strecker a tubular stent comprises knitted metal or plastic filaments. The delivery system includes a balloon catheter and a coaxial, radially flexible sheath for overlying the stent in a compact form carried on the balloon. The catheter supports and carries the compacted stent to a placement. The sheath inhibits premature deployment and facilitates transit of the stent during insertion. After moving the sheath axially with respect to the catheter, expansion of the balloon enlarges the stent and urges it into contact with surrounding vessel walls. Deflation of the balloon frees it from the stent and enables withdrawal of the delivery system from the patient.
Savin et al. also disclose a delivery system with a catheter having an expansible distal portion that carries a stent in its compacted configuration. An axially flexible sleeve overlies portions of the stent and slides axially away from the stent in response to expansion of an expansible portion of the system underlying the stent and consequential expansion of the stent. The sleeve protects the vessel and the stent during insertion without substantially inhibiting deployment of the stent.
The following United States Letters Patents describe various types of such systems for the percutaneous insertion of grasping devices, such as retrieval baskets:
Segura et al. disclose a delivery system for a retrieval basket for stones and the like from the kidneys, the ureter or the biliary duct. The delivery system comprises an elongated tube generally inserted through the working channel of an endoscope. A physician selectively positions the retrieval basket that is in a compact condition within a distal end of the tube. Then the physician extends the basket from the distal end of the tube so it expands into a bulbous shape. In one embodiment the tube includes an inner wire coil that surrounds the basket in its compact form. The coil provides flexibility and strength at the distal end.
Grayhack et al. disclose another system for a delivery and deployment with an elongated smooth outer tubular sheath overlying and containing a stranded wire cable terminating in a distal protective tip at the working or distal end of the device. When a user distally extends the cable, the individual spring wire strands at the distal end expand to form a retrieval basket. Retraction of the cable into the tube returns the distal end of the cable to its compact form. The catheter portion surrounding the retrieval basket in its retracted and compact state comprises an expandable distal end that facilitates the capture of a stone.
Vena cava filters differ from stents and retrieval baskets primarily because vena cava filers include legs that terminate in pointed, outwardly facing hooks. Typically vena cava filters are expanded in a free state. Consequently when a vena cava filter is constrained in its compact configuration, internal stresses urge the free ends of the hooks radially outward and attempts to drive the hooks into any constraining member. As will be apparent, the delivery systems in the foregoing patents are not adapted for delivery vena cava filters because the hooks will penetrate surrounding tubing, catch between adjacent coil turns or otherwise become fixed in the distal end. The occurrence of any of these conditions can increase the complexity of the procedure or render the instrument completely useless. Consequently special delivery systems or vena cava filters formed of special materials or in special shapes have been used for the percutaneous insertion of vena cava filters, such as disclosed in the following patents:
Kimmell, Jr. discloses a delivery system with an elongated metal carrier disposed at the distal end of a catheter. The filter overlies the carrier and a locking collar overlies the hooks to retain the legs against the carrier in a compact configuration. Actuating a syringe increases the pressure on a piston in the carrier to drive a distal portion of the carrier and the filter distally with respect to the delivery system whereby the hooks move away from the locking collar and expand into contact with the walls of the vessel.
Simon discloses a system for delivering a Nitinol wire vena cava filter. The filter is formed along an axis and has a low temperature compact shape in which the legs cross the axis so the hooks extend upwardly toward the axis and do not engage the delivery system. Upon warming in the lumen at the delivery site the filter expands into its desired shape whereby the hooks penetrate and lock into the surrounding vessel. The delivery system includes apparatus for providing a cold infusion drip for maintaining a cool temperature in the catheter during the positioning of the filter.
In Palmaz a vena cava filter comprises a material which has essentially no expansion forces in its compacted form but will lock into and expanded position. A balloon expands the filter after a sheath is removed. As there are no internal forces, the hooks do not penetrate the walls of the delivery system during transport.
Herms et al. disclose a delivery system with a first outer catheter and an overlying sheath that are positioned with their respective distal ends proximate a delivery site. An insertion catheter carries a cartridge with a filter in a compact form and positioned with the hooks at the distal end. The hooks do not tend to embed in the catheter wall and can move distally with respect to the cartridge. This delivery system is useful in therapies where apex of the filter points proximally of the hooks, typically upstream with respect to blood flow.
Palestrant discloses, in one embodiment, a system in which a catheter tube is prepositioned in a patient. Then the filter is pushed through the entire length of the catheter with the legs compressed into a compact form. The filter has two portions including a distal portion that expands to form a mesh as two spaced connections are drawn together. The leg portions extend proximally from one connector and spring into an open or expanded position when they exit the distal end of the catheter.
Gory et al. discloses a catheter delivery system for deploying a reversible vena cava filter. The legs of the vena cava filter parallel or converge on the catheter axis so the ends of the filter legs do not snag or catch an inner catheter surface. This allows the vena cava filter to be inserted relatively simply.
FIG. 1 depicts another embodiment of a prior art delivery system 1 for use with a long, radially flexible tube 2 that houses a self-expansible vena cava filter 3 in a compact form in a defined cavity 6 of a coaxial metal tube or sleeve 5 that extends from the distal end of the tube 2. The sleeve thus overlies the filter 3 within the defined cavity 6. Manipulation of a slide portion (not shown) displaces the filter 3 distally relative to the sleeve 5 and the tube 2 to urge the filter 3 through a distal end 7 into a patient's lumen 8. A previously positioned guidewire (not shown) is generally used to position the distal end of the delivery system at the delivery site. The sleeve 5 is formed of a material that hooks 9 at the end of the vena cava filter 3 can not perforate or otherwise penetrate during insertion or deployment of the vena cava filter 3.
The foregoing delivery systems generally effectively and reliably deploy vena cava filters carried within the sleeve. However, their use can be limited, as for example, by the inflexibility of the sleeve of the delivery system of FIG. 1 and hence of the distal end of the tube, that makes it difficult to negotiate tortuous paths frequently encountered during a percutaneous insertion. If a physician discovers such a tortuous path, the physician may be forced to discontinue the procedure and elect an alternative procedure, such as major surgery with its additional risks and trauma to a patient. Alternatively, the physician may elect to force the distal end along such path, notwithstanding possible damage to vessels, "kinking" of the distal end or both. "Kinking" can permanently deform or bend the surrounding sleeve and further complicate navigation of the distal end. "Kinking" can also cause the tube essentially to double over proximally of the sleeve. "Kinking" both further complicates the procedure and increases the time necessary to perform the procedure.
Collectively the prior art delivery systems may require a specially formed filter, may require pushing implements to displace a vena cava filter through portions or the entire length of a catheter. For example, Gory et al. require the use of a vena cava filter that does not include sharp hooks that can penetrate or abrade a surrounding sleeve. Simon is limited to a vena cava filter formed of a two-phase material so that the hooks thereof do not imbed in the walls of the catheter prior to delivery thereof. The vena cava filters disclosed by Simon and Palestrant must be pushed through a catheter from the proximal to the distal end. Palmaz uses a special vena cava filter structure that locks in an expanded shape after inflating a balloon. Palestrant discloses a vena cava filter located in the distal end of a catheter, but in the apparatus an outer catheter must be prepositioned.
The prior art thus fails to provide a delivery system simply manufactured, simply used, reliable system for efficiently transporting through and deploying in a patient's lumen a self-expanding vena cava filter having radially extending hook portions that contact the walls of the delivery system. The prior art also fails to provide a delivery system that transports such a vena cava filters within a distal end section to enable relatively immediate delivery of the vena cava filter while enabling radial flexion of the distal end section. The delivery systems of the prior art also fail to imperviously encase radially extending abrading portions of such devices while enabling relatively free radial deflection along the delivery system contiguous with the device.